U.S. Pat. No. 1,250,238 to Spitzglass for a Pitot Tube discloses a method of measuring fluids by means of a Pitot tube which transmits the pressure equivalent of the velocity of a fluid in a pipe or conduit to suitable outside means for indicating or recording the volume of fluid flowing through the conduit. The principal object of the invention is to provide an improved form of Pitot tube which transmits pressure difference actuated by the mean velocity of a fluid throughout the entire cross-sectional area of the pipe or conduit in contradistinction to the average velocity in the pipe.
U.S. Pat. No. 1,645,449 to Proebstel for a Multiple Pitot and Piezometer Tube for Measuring the Flow of Water through Closed Conduits teaches the taking of instantaneous readings of a plurality of Pitot nozzles placed within a closed conduit, and the use of a camera to record those readings.
U.S. Pat. No. 4,344,330 to Renken et al. for an Average Fluid Flow Sensor discloses a sensor for providing a differential pressure signal indicative of the average relative rate of flow of a fluid through a duct. Two tubular members are provided, each of which are formed in a loop oriented transverse to the fluid flow and each having a plurality of spaced-apart orifices along their length. In one of the tubular members, the orifices face upstream toward the impinging fluid flow; in the other, the orifices face downstream. The difference between the pressures developed within the two tubular members as a result of the orientation of these orifices relative to fluid flow is indicative of the average rate of fluid flow in the duct.
U.S. Pat. No. 5,123,288 to Tench et al. for an Averaging Pitot Probe teaches a flowmeter to measure speed of gas flow along a pipe comprising a gas flow sensor connected by tubing with an averaging Pitot probe formed by first and second tubes of circular cross-section disposed side by side and closed at their one and the same ends and mounted in a gas tight manner in the wall of the pipe. The two tubes are identical in shape and dimensions and each has four circular holes through its tube wall. All the holes are of the same shape and size, and each has a diameter in the range 0.4 mm to 1.00 mm. The internal diameter of each tube is at least 1.59 mm, and the ratio of the cross-sectional area of each tube to the cross-sectional area of each hole is at least 9:1. The positions of the holes in one tube are identical to the positions of the holes in the other tube except that the holes in the first tube face directly upstream with respect to the gas flow whilst the holes in the second tube face directly downstream. With respect to an imaginary plane P between the tubes, the first tube is symmetrical with the second tube. The speed of gas flow to be measured is preferably in the range of 0.3 to 10.00 m/s, and the gas is at or about atmospheric pressure.
U.S. Pat. No. 5,736,651 to Bowers for a High Temperature Gas Flow Sensing Element describes a sensing element having a housing with similar internal dimensions as the fluid conduit, whether round or rectangular. An interior flow conditioner is affixed at the inlet of the flow element. A total pressure sensing Pitot tube array is affixed traversing the interior cross sectional area of flow element for sensing the total pressure of fluid flowing into the flow element, and a static pressure sensing Pitot tube array is also affixed traversing the interior cross sectional area of the flow element for sensing the average static pressure within the flow element. The Pitot tubes and pressure sensing tubes are affixed at four places, two shell penetrations and two places at the manifolds, regardless of manifold design or the element shape. To prevent material stress and fatigue and leakage that can result from the different expansion rates of differing materials under high gradient temperature cycling, a high temperature packing, such as a ribbon packing or packing ring made of pliable material resistant to high temperatures, is used in place of the ferrule portion of a compression nut and fitting arrangement. Exterior first and second instrument taps are provide for connection of each array respectively to a differential pressure instrument for indicating flow rate and/or transmitting a flow rate signal. Further, exterior array access ports are provided to permit cleaning of each Pitot arrays should they become plugged with particulates.
U.S. Pat. No. 6,237,426 to Gryc et al. for an Airflow Sensor discloses an multi-point, center-averaging airflow sensor comprises a plurality of upstream airflow sensing tubes extending radially from a central hub having a total pressure averaging chamber and a static pressure averaging chamber. The airflow sensing tubes are each provided with at least one total pressure port located inwardly of the outer end of the tubes to minimize error caused by total pressure measurements taken near the inner walls of the conduit in which the sensor is installed. The sensor has static pressure ports located in the side surface of the hub which are shielded from upstream air flow by the tubes and which are preferably at least partially shielded from damper back pressure by notched reinforcing blades provided along the length of the airflow sensing tubes.
There are many prior designs that employ multiple averaging Pitot tubes that sample air pressures at multiple points within a bounded path, and average these multiple readings by providing fluid communication between all sensing ports to obtain a total average pressure, usually an impact pressure caused by gas impacting sensing ports facing the flow of gas, and a static pressure detected by sensing ports facing downstream of the flow of gas. These average pressures can be translated into average velocity and from velocity into average flow volume. Most prior art references specify a number of and spacing of sensing ports on the Pitot tubes in a manner to collect gas pressure samples from specific regions of the bounded path, as shown in the patents to Tench et al. and Spitzglass, supra. Most prior art references also use a centrally located chamber or plenum to collect the multiple point pressure readings into an average total pressure. Some terms used with the prior art are “multi-point center averaging,” “branch averaging Pitot,” and “plurality of pressure sensors.”
There are numerous problems with these prior designs, including, but not limited to, the following:                1. The most important criteria when observing something is to do so without disturbing the object being observed. A flow velocity profile of a fluid or gas in a straight bounded path shows the highest velocity to be near the center of the path. This flow velocity profile is illustrated in FIG. 1 of the patent to Proebstel, and usually represents a “D” shape profile in a horizontal conduit. Any object in the center of, or crossing through the center of, a bounded path disturbs the flow where the flow velocity is usually greatest. This is the worst place to disrupt a flow path, and creates undesired turbulence. Turbulence usually adversely affects the performance of the flow measuring device and all supporting equipment (e.g., electronic pressure transducers).        2. As the temperature of the gas flow increases or decreases, the size of the bounded path may increase or decrease by thermal expansion of the materials used. With some prior art devices where opposing walls are mechanically connected by a pressure sensing structure (e.g., Gryc et al.) or supporting structure (e.g., Renken et al.), structural failure may result from unequal expansion of boundaries and connecting structures. Bowers addresses this expansion problem with a system of bushings that allow the boundary to move independently of other structures, but this can lead to changes in the critical distance between the outer-most sensing ports and the boundaries of the path where changes in velocity over distance from the boundary are greatest. These high levels of change in velocity over distance from the boundary are again illustrated in FIG. 1 of Proebstel, showing the “D” shape of a typical velocity profile of a fluid in a round conduit.        3. Pressure sensing ports that face oncoming particulated gasses are subject to clogging and damage from particles, causing false readings or rendering the device inoperable when attempting to measure particulated gasses. A grey medium can be defined as a gas or fluid containing essentially round shaped particles that do not have sticking, clinging or accumulative properties. Examples include sawdust, metal filings, plastic filings, sand, silt, and some types of smoke.        4. Most prior designs are fixed and cannot be customized during manufacture.        5. Most prior designs are mono-directional.        
The foregoing patents reflect the current state of the art of which the present inventor is aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicant's acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.